Two Stage Condensing and Metering Refrigeration System

ABSTRACT

A refrigeration system, includes a main refrigeration system. The main refrigeration system includes a main refrigerant, a main compressor, a main condenser coil, a pre-metering device, a main metering device, a main evaporator, and a secondary refrigeration system. In flow sequence, the main refrigerant within the main refrigeration system is compressed by the main compressor, condensed by the main condenser coil, dropped in pressure by the pre-metering device, cooled by the secondary refrigeration system, dropped in pressure by the main metering device, vaporized by the main evaporator and returned to the main compressor. The secondary refrigeration system includes a secondary refrigerant, a secondary compressor, a secondary condenser coil, a secondary metering device, a secondary evaporator having a main refrigerant cooling path and a secondary refrigerant evaporator path in heat transfer communication. In flow sequence, the secondary refrigerant in the secondary refrigeration system is compressed by the secondary compressor, condensed by the secondary condenser coil, dropped in pressure by the secondary metering device, and vaporized by the evaporator path by heat transfer from the cooling path carrying the main refrigerant, and returned to the secondary compressor. The main condenser coil and the secondary condenser coil are located together in a housing to be cooled by the same flowing media. The secondary evaporator is a co-axial pipe heat exchanger.

BACKGROUND OF THE INVENTION

The present invention is directed to refrigeration systems, particularly to an improved mechanical refrigeration system.

A conventional mechanical refrigeration system 20 is shown in FIG. 3. The refrigeration system comprises a compressor 24, a condenser 26 having a condenser coil 27, a metering device 28 such as an expansion valve, and an evaporator 30 having an evaporator coil 32. Refrigerant gas is drawn into the compressor at point J, is compressed at point A and delivered into the condenser coil at point B. Air can be blown over the condenser coil, or simply ambient air surrounds the condenser coil, wherein the air absorbs heat from the refrigerant within the coil and the refrigerant is thus cooled. The refrigerant gas is condensed into a liquid within the condenser. The liquid refrigerant from the condenser is subcooled and delivered into the metering device at point F and then enters into the evaporator at point G. In the evaporator 30, air is typically blown over the evaporator coil, or simply ambient air surrounds the evaporator coil 32. The air is cooled as the refrigerant within the coil 32 absorbs heat from the air and the liquid refrigerant thus vaporizes (boils) into a gas. The refrigerant gas is drawn into the compressor at point J, defining a complete cycle of refrigerant flow.

The pressure-enthalpy chart corresponding to the operation of this conventional refrigeration systems is shown in FIG. 4. In this figure, point I represents the refrigerant entering into the compressor 24, point A represents refrigerant leaving the compressor 24 and delivered into the condenser coil 27, point F represents refrigerant leaving the condenser coil 27 and entering into the metering device 28. Point G represents refrigerant entering into the evaporator coil 32.

FIG. 4 shows that, for the regular refrigeration systems, it is the portion of G-I that is the net refrigeration effect, and the portion of P-G is the flash gas, which represents the portion of the liquid refrigerant becoming flash gas when it enters into the evaporator. The portion of refrigerant flash gas does not play a role in the refrigeration effect and lowers the refrigeration efficiency. Experimental data shows that for R404a refrigerant used in freezers, the net efficiency of refrigeration is only about 40%, and about 60% of refrigerant becomes flash gas. This is why conventional refrigeration systems have low efficiency.

The present inventor has recognized that it would be desirable to provide an improved refrigeration system that had an increased energy efficiency. The present inventor has recognized that it would be desirable to provide an improved refrigeration system that was compatible with a variety of refrigerants, and a variety of refrigeration systems, products, and equipment.

SUMMARY

A mechanical refrigeration system of the exemplary embodiment of the invention, with two stages of refrigerant condensing and metering, is provided wherein a second stage functions to lower the temperature of liquid refrigerant before the refrigerant enters an evaporator of a first stage. The refrigeration systems of the exemplary embodiment of the invention, with two stages of refrigerant condensing and metering, will have significantly higher COP (Coefficient of Performance) and therefore will have significantly higher energy efficiency compared to conventional refrigeration systems. For example, freezers using R404a refrigerant, using the exemplary embodiment of the invention, with two stages of refrigerant condensation and metering, could have 30% or more in added energy efficiency. For other refrigeration devices or other refrigerants, the results in energy saving would be similar.

The exemplary embodiment of the invention provides a refrigeration system with two stages of refrigerant condensing and metering, with the second stage being a mechanical refrigerant cooler. A first stage or main refrigeration system comprises a main compressor, a main condenser, a pre-metering device, a main metering device, and a main evaporator. A main refrigerant gas is drawn into the main compressor, then is compressed and delivered into the main condenser, wherein the main refrigerant gas is cooled by an external media such as, for example, ambient air or air blown over a condenser coil containing the main refrigerant; the main refrigerant condenses into a liquid, leaves the main condenser and enters into the pre-metering device. The main refrigerant exiting the pre-metering device will have a lower pressure, and some refrigerant vaporizes because of the lowered main refrigerant pressure.

An exemplary refrigeration system of the invention can include a main refrigeration system including a main refrigerant, a main compressor, a main condenser coil, a pre-metering device, a main metering device, a main evaporator, and a secondary refrigeration system.

An outlet of the main compressor is main-refrigerant-flow-connected to the main condenser coil, the main condenser coil is main-refrigerant-flow-connected to the pre-metering device, the pre-metering device is main-refrigerant-flow-connected to the secondary refrigeration system, the secondary refrigeration system is main-refrigerant-flow-connected to the main metering device, the main metering device is main-refrigerant-flow-connected to the main evaporator, and the main evaporator is main-refrigerant-flow-connected back to an inlet of the main compressor.

In flow sequence, the main refrigerant within the main refrigeration system is compressed by the main compressor, condensed by the main condenser coil, dropped in pressure by the pre-metering device, cooled by the secondary refrigeration system, dropped in pressure by the main metering device, vaporized by the main evaporator and returned to the main compressor defining a main refrigeration system cycle.

The secondary refrigeration system includes a secondary refrigerant, a secondary compressor, a secondary condenser coil, a secondary metering device, a secondary evaporator having a cooling path such as a coil or set of tubes or a shell, and an evaporator path, such as a coil or set of tubes or a shell, in heat transfer communication. In flow sequence, the secondary compressor is secondary-refrigerant-flow-connected to the secondary condenser coil; the secondary condenser coil is secondary-refrigerant-flow-connected to the secondary metering device; the secondary metering device is secondary-refrigerant-flow-connected to the evaporator path within the secondary evaporator; and the evaporator path is secondary-refrigerant-flow-connected to the secondary compressor, defining a secondary refrigeration system cycle.

The pre-metering device of the main refrigeration system is main-refrigerant-flow-connected to an inlet of the cooling path in the secondary evaporator of the secondary refrigeration system, wherein an outlet of the cooling path is main-refrigerant-flow-connected to the main metering device of the main refrigeration system.

In flow sequence, the secondary refrigerant in the secondary refrigeration system is compressed by the secondary compressor, condensed by the secondary condenser coil, dropped in pressure by the secondary metering device, and vaporized by the evaporator path by heat transfer from the cooling path carrying the main refrigerant, and returned to the secondary compressor defining a secondary refrigeration system cycle.

The main condenser coil and the secondary condenser coil can be located together in a housing to be cooled by the same flowing media. The secondary evaporator can comprise a co-axial pipe heat exchanger.

The main refrigerant, being in both liquid and gas phases, is conducted into the secondary refrigeration system to obtain a subsequent main refrigerant condensation and to also further lower the temperature of the main refrigerant by a mechanical refrigerant cooler. Any gas portion of the main refrigerant is condensed into liquid again in the secondary refrigeration system, and the main refrigerant liquid is cooled to a lower temperature than the temperature at the exit of the main condenser coil. To accomplish this cooling, the main refrigerant, going through the pre-metering device, is delivered into a heat exchanger in the secondary refrigeration system to transfer heat from the main refrigerant to a secondary refrigerant. The heat exchanger comprises an evaporator for the secondary refrigerant in the secondary refrigeration system. The main refrigerant liquid from the heat exchanger is then returned to the main refrigeration system and to the main metering device and then into the main evaporator.

Within the main evaporator, the main refrigerant absorbs the heat of the external media being cooled, for example ambient air or air blown over the evaporator coil, which cools the media, and the main refrigerant vaporizes (boils) into a gas. The main refrigerant gas is again drawn into the main compressor, defining a main refrigerant flow cycle.

The pre-metering device is designed such that the refrigerant leaving the main condenser will be in substantially a liquid phase, to avoid excessive main refrigerant gas being condensed in the secondary refrigeration system, which would result in a lower performance of the overall refrigeration system.

The refrigeration system of the exemplary embodiment of the invention, with two stages of refrigerant condensing and metering, achieves a higher efficiency of refrigeration by lowering main refrigerant temperature after the refrigerant condenses in the main condenser. The refrigeration system of the exemplary embodiment of the invention, with two stages of refrigerant condensing and metering, can also achieve high energy efficiency, high performance, and longer working life of refrigeration systems, products, and equipment.

The refrigeration system of the exemplary embodiment of the invention, with two stages of refrigerant condensing and metering, is usable for a variety of refrigeration systems, products, and equipment using a variety of refrigerants.

Numerous other advantages and features of the present invention will be become readily apparent from the following detailed description of the invention and the embodiments thereof, and from the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a refrigeration system of the present invention;

FIG. 2 is a schematic view of a portion of the secondary refrigeration system which is for providing secondary condensation of the main refrigerant in the main refrigerant system of FIG. 1;

FIG. 2A is a schematic view of a condenser shown in FIG. 2;

FIG. 2B is a schematic view of another embodiment secondary evaporator in the form of a co-axial pipe refrigerant evaporator-heat exchanger;

FIG. 2C is a schematic view of a portion of the co-axial pipe refrigerant evaporator-heat exchanger shown in FIG. 2B;

FIG. 2D is a schematic cross section view taken generally along line 2D-2D of FIG. 2C;

FIG. 3 is a schematic diagram of a conventional refrigeration system;

FIG. 4 is a pressure/enthalpy chart for a conventional refrigeration system; and

FIG. 5 is a pressure/enthalpy chart for the system of FIGS. 1 and 2.

DETAILED DESCRIPTION

While this invention is susceptible of embodiment in many different forms, there are shown in the drawings, and will be described herein in detail, specific embodiments thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiments illustrated.

The exemplary embodiment of the invention provides a refrigeration system 50 with two stages of refrigerant condensing and metering, having a main refrigeration system and a secondary refrigeration system.

A two stage condensing and metering refrigeration system is shown in FIG. 1.

FIG. 1 illustrates the overall refrigeration system 50 comprises a main refrigeration system 52 having main compressor 54, a pre metering device 66, a main metering device 76, a main evaporator 80 having an evaporator coil 84; and a combination condenser 58. The condenser has two coils 60, 62. The coil 60 is for the main refrigerant, and the coil 62 is for a secondary refrigerant system 70 described below. The two coils are located within the same housing and are cooled together by a common media, such as blowing air across the coils, driven by a fan.

The combination condenser 58 having two coils has the advantage of small size, low costs compared to two separate condensers. FIG. 2A shows the dual coil condenser 58 in more detail. An air fan 189 can be employed to blow cooling air across both coils 60, 62.

In FIG. 1, a main refrigerant gas is drawn into the main compressor 54 at point J, then is compressed at point A and delivered into the combination condenser coil 60 at point B. From the combination condenser coil 60, the main refrigerant contained therein transfers heat to a media, such as air, by ambient air or by air being blown over the condenser coil 60, which heats the air and condenses the main refrigerant. The main refrigerant gas condenses into a liquid, leaves the main condenser coil 60 and enters into the pre-metering device 66 at point F where the pressure of the main refrigerant is lowered. The main refrigerant from the pre-metering device 66 will have a lower temperature, and some refrigerant vaporizes because the refrigerant pressure is lowered. The main refrigerant, in both liquid and gas phases, is conducted into the secondary refrigeration system 70 at point F′.

A secondary refrigeration system 70 comprises a secondary mechanical refrigeration system that acts as a refrigerant cooler and condenser. In the secondary refrigeration system 70, the main refrigerant gas is again condensed into liquid with a lower temperature than the temperature at the exit of the main condenser coil 60 at point F. The liquid main refrigerant from the secondary refrigeration system 70, at point H, enters the main metering device 76 and then enters the main evaporator coil 84 at point G′. Within the main evaporator coil 84 the refrigerant absorbs the heat of a media to be cooled, such as air, by ambient air or by air being blown over the evaporator coil 84, which cools the air, and the refrigerant vaporizes into gas by absorbing heat from the air. The main refrigerant gas from the evaporator 80 at point I is again drawn into the main compressor 54 at point J, defining a complete refrigerant flow cycle.

The pre-metering device 66 is designed such that the refrigerant leaving the main condenser coil 60 will substantially be in a liquid phase, to avoid refrigerant gas being condensed in the secondary refrigeration system 70, which would result in a lower performance of the overall refrigeration system.

The pre-metering device 66 and the secondary refrigeration system 70 is shown in FIG. 2. The secondary refrigeration system 70 is also a complete mechanical refrigeration system, comprising a secondary compressor 154, the condensing coil 62 of the combination condenser 58, a secondary metering device 176, and a secondary refrigerant evaporator-heat exchanger 180.

The secondary refrigeration system 70 works as follows: a secondary refrigerant gas is drawn into the secondary compressor 154 at point K, is then compressed and delivered into the secondary condenser coil 62 in the combination condenser 58 at point L, wherein the secondary refrigerant gas condenses into a liquid. The liquid secondary refrigerant is delivered into the secondary metering device 176 at point M, then enters into the co-axial pipe refrigerant evaporator-heat exchanger 180 at point N. In the co-axial pipe refrigerant evaporator-heat exchanger 180 the secondary liquid refrigerant absorbs heat of the main liquid refrigerant from the pre-metering device 66 and the secondary refrigerant vaporizes into gas. The secondary refrigerant gas leaves the evaporator-heat exchanger 180 at point P then enters the secondary compressor 154 at point K, defining a complete refrigerant flow cycle.

Rather than absorbing heat from air, by ambient air or by air being blown over the evaporator coil or set of tubes, the evaporator coil 184 of the co-axial pipe refrigerant evaporator 180 absorbs heat from the main refrigerant flowing in the spacing between inner pipe coil 184 and outer coil 188 containing the main refrigerant. In this regard, the co-axial pipe refrigerant evaporator-heat exchanger is a heat exchanger functioning to transfer heat from the main refrigerant to the secondary refrigerant.

FIGS. 2B-2D illustrate the use of a co-axial pipe heat exchanger as the evaporator 180. The secondary refrigerant is carried within an inner pipe 184, and an outer pipe 188 carries the main refrigerant. The inner and outer pipes are arranged in a serpentine fashion to make the heat exchanger 180 compact. FIG. 2C shows a simple version of the arrangement with only one turn. In practice there would be multiple turns as shown in FIG. 2B. As shown in FIG. 2C the flow direction in the inner and outer pipes is counter flow, with a, b being the flow directions in the inner pipe and c, d being the flow directions in the outer pipe, direction a being counter to direction c and direction b being counter to direction d.

The use of a co-axial pipe heat exchanger as the secondary refrigerant evaporator-heat exchanger 180 is advantageous for reducing the size of the secondary refrigerant evaporator-heat exchanger, providing a high efficiency in heat transfer and using less material in construction.

The liquid main refrigerant from the pre metering device 66 enters into the cooling coil 188 of the secondary evaporator-heat exchanger 180 at point F′ in FIG. 1, and FIG. 2 to transfer its heat to the secondary refrigerant, and the main refrigerant gas, because of lower pressure, is again condensed into a liquid phase, and then leaves the cooling coil at point H in FIG. 1 and FIG. 2 to enter the main metering device 76 and the main evaporator coil 84.

The metering devices 66, 76, 176 can be configured as an expansion valve, an orifice, capillary tubes, or any other known metering devices which can be used to drop refrigerant pressure across the metering device.

The main refrigerant and the secondary refrigerant can be the same refrigerant or different refrigerants. For example, the main refrigerant could be R404a and the secondary refrigerant can be R134a.

FIG. 5 shows the pressure-enthalpy chart of the refrigeration systems of two stages of refrigerant condensing and metering. In the figure, the point F represents the refrigerant leaving the main condenser, because of the pre-metering device operation, the refrigerant at the point F is in a liquid state. The liquid main refrigerant passes through the pre-metering device 66, at point F′ in FIG. 5. At this point some portion of refrigerant becomes flash gas because of the lowered pressure. The refrigerant of both liquid and gas phase enters into the secondary refrigeration system 70 wherein the gas is again condensed into a liquid at point H in FIG. 5. The main refrigerant from the secondary refrigeration system 70 at point H in FIG. 5 goes through the main metering device 76 at point G in FIG. 5 then enters into the coil 84 of the main evaporator 80. In the main evaporator 80, the main refrigerant vaporizes into a gas and will be drawn again into the main compressor 54, defining a complete refrigerant working cycle.

Because of the use of pre-metering device 66 and the secondary refrigeration system 70, the effect of the refrigeration is extended to IG′, which is significantly longer than the portion of IG of FIG. 4. It is because of this feature that the refrigeration system with two stage of refrigerant condensing and metering has significantly higher efficiency of refrigeration and energy use.

Exemplary Embodiment for Freezers

-   -   1. The main refrigeration circuit (freezer):         -   Main refrigerant: R-404a         -   Environment room temperature 79 F         -   Main refrigerant pressure in main Condenser: 210 psig         -   Temperature at the point of the main condenser (point F in             FIG. 1): 90 F         -   Main refrigerant pressure in main evaporator: 8.9 psig         -   Main refrigerant evaporating temperature in main evaporator:             −32 F     -   2. The secondary refrigeration circuit:         -   Secondary refrigerant: R-134a         -   Environment room temperature 79 F         -   Secondary refrigerant pressure in secondary Condenser: 105             psig         -   Secondary refrigerant temperature at the point of the             secondary condenser (point M in FIG. 2): 85 F         -   Secondary refrigerant pressure in secondary evaporator: 26             psig         -   Secondary refrigerant evaporating temperature in secondary             evaporator: 30 F

Expected Data for Freezers

-   -   1. The main refrigeration circuit:         -   Main refrigerant R-404a         -   Environment room temperature from 40 F˜103 F         -   Main refrigerant pressure in main evaporator: 7.4 psig         -   Main refrigerant evaporating temperature in main evaporator:             −35 F     -   2. The secondary refrigeration circuit:         -   Secondary refrigerant: R-134a         -   Environment room temperature from 40 F to 103 F         -   Secondary refrigerant pressure in secondary evaporator: 26.1             psig         -   Secondary refrigerant evaporating temperature in secondary             evaporator: 30 F

From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred. 

The invention claimed is:
 1. A refrigeration system, comprising: a main refrigeration system including a main refrigerant, a main compressor, a main condenser coil, a pre-metering device, a main metering device, a main evaporator, and a secondary refrigeration system; wherein an outlet of the main compressor is main-refrigerant-flow-connected to the main condenser coil, the main condenser coil is main-refrigerant-flow-connected to the pre-metering device, the pre-metering device is main-refrigerant-flow-connected to the secondary refrigeration system, the secondary refrigeration system is main-refrigerant-flow-connected to the main metering device, the main metering device is main-refrigerant-flow-connected to the main evaporator, and the main evaporator is main-refrigerant-flow-connected back to an inlet of the main compressor; wherein, in flow sequence, the main refrigerant within the main refrigeration system is compressed by the main compressor, condensed by the main condenser coil, dropped in pressure by the pre-metering device, cooled by the secondary refrigeration system, dropped in pressure by the main metering device, vaporized by the main evaporator and returned to the main compressor; wherein the secondary refrigeration system includes a secondary refrigerant, a secondary compressor, a secondary condenser coil, a secondary metering device, a secondary evaporator having a cooling path and evaporator path therein in heat transfer communication; the secondary compressor is secondary-refrigerant-flow-connected to the secondary condenser coil, the secondary condenser coil is secondary-refrigerant-flow-connected to the secondary metering device, the secondary metering device is secondary-refrigerant-flow-connected to the evaporator path within the secondary evaporator, the evaporator path is secondary-refrigerant-flow-connected to the secondary compressor; wherein the pre-metering device of the main refrigeration system is main-refrigerant-flow-connected to an inlet of the cooling path in the secondary evaporator of the secondary refrigeration system, wherein an outlet of the cooling path is main-refrigerant-flow-connected to the main metering device of the main refrigeration system; wherein, in flow sequence, the secondary refrigerant in the secondary refrigeration system is compressed by the secondary compressor, condensed by the secondary condenser coil, dropped in pressure by the secondary metering device, and vaporized in the evaporator path by heat transfer from the cooling path carrying the main refrigerant, and returned to the secondary compressor; wherein the main condenser coil and the secondary condenser coil are located together in a housing to be cooled by the same flowing media.
 2. The refrigeration system according to claim 1, wherein the secondary evaporator comprises a co-axial pipe heat exchanger.
 3. The refrigeration system according to claim 2, wherein an inside pipe of the co-axial pipe heat exchanger carries the secondary refrigerant, and an outside pipe of the co-axial pipe heat exchanger, surrounding the inside pipe, carries the main refrigerant.
 4. The refrigeration system according to claim 1, wherein the main evaporator comprises a co-axial pipe heat exchanger.
 5. A refrigeration system, comprising: a main refrigeration system including a main refrigerant, a main compressor, a main condenser coil, a pre-metering device, a main metering device, a main evaporator, and a secondary refrigeration system; wherein an outlet of the main compressor is main-refrigerant-flow-connected to the main condenser coil, the main condenser coil is main-refrigerant-flow-connected to the pre-metering device, the pre-metering device is main-refrigerant-flow-connected to the secondary refrigeration system, the secondary refrigeration system is main-refrigerant-flow-connected to the main metering device, the main metering device is main-refrigerant-flow-connected to the main evaporator, and the main evaporator is main-refrigerant-flow-connected back to an inlet of the main compressor; wherein, in flow sequence, the main refrigerant within the main refrigeration system is compressed by the main compressor, condensed by the main condenser coil, dropped in pressure by the pre-metering device, cooled by the secondary refrigeration system, dropped in pressure by the main metering device, vaporized by the main evaporator and returned to the main compressor; wherein the secondary refrigeration system includes a secondary refrigerant, a secondary compressor, a secondary condenser coil, a secondary metering device, a secondary evaporator having a cooling path and evaporator path therein in heat transfer communication; the secondary compressor is secondary-refrigerant-flow-connected to the secondary condenser coil, the secondary condenser coil is secondary-refrigerant-flow-connected to the secondary metering device, the secondary metering device is secondary-refrigerant-flow-connected to the evaporator path within the secondary evaporator, the evaporator path is secondary-refrigerant-flow-connected to the secondary compressor; wherein the pre-metering device of the main refrigeration system is main-refrigerant-flow-connected to an inlet of the cooling path in the secondary evaporator of the secondary refrigeration system, wherein an outlet of the cooling path is main-refrigerant-flow-connected to the main metering device of the main refrigeration system; wherein, in flow sequence, the secondary refrigerant in the secondary refrigeration system is compressed by the secondary compressor, condensed by the secondary condenser coil, dropped in pressure by the secondary metering device, and vaporized by the evaporator path by heat transfer from the cooling path carrying the main refrigerant, and returned to the secondary compressor; wherein the secondary evaporator comprises a co-axial pipe heat exchanger.
 6. The refrigeration system according to claim 6, wherein an inside pipe of the co-axial pipe heat exchanger carries the secondary refrigerant, and an outside pipe of the co-axial pipe heat exchanger, surrounding the inside pipe, carries the main refrigerant. 